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Dairy products are a primary source of c9, t11-CLA, an anti-carcinogenic agent, in the diet of humans. The t10, c12-CLA isomer, typically in trace amounts in bovine milk fat, also may benefit human health. Four cows received abomasal infusions of c9, t11-CLA or t10, c12-CLA to obtain milk fat used to prepare butter and yogurt with enhanced c9, t11-CLA or t10, c12-CLA content. Human subjects (3 males, 3 females, ages 22 to 29) received CLA-enhanced butter and yogurt (14% of total kcal) in a crossover study with 2-wk periods. Prior to the study (2 wk) and during a 2-wk washout period between the experimental periods, subjects received butter and yogurt without enhanced CLA content. Blood samples were obtained at 0, 2, 4, 6, and 8 wk relative to the start of the first experimental period. The t10, c12- CLA isomer was detected in plasma (1.32 ug/mL) only when dairy products with enhanced t10, c12-CLA was consumed. Baseline c9, t11-CLA was 6.94 ug/mL plasma during control periods, but increased to 8.95 ug/mL when dairy products with enhanced c9, t11-CLA content were consumed. Results indicated concentrations of CLA isomers in human plasma respond to small changes in daily intake of the isomers in dietary sources.